Ternary complex dissociation kinetics contribute to mutant-selective EGFR degradation.

Targeted degradation of proteins by chimeric heterobifunctional degraders has emerged as a major drug discovery paradigm. Despite the increased interest in this approach, the criteria dictating target protein degradation by a degrader remain poorly understood, and potent target engagement by a degrader does not strongly correlate with target degradation. In this study, we present the biochemical characterization of an epidermal growth factor receptor (EGFR) degrader that potently binds both wild-type and mutant EGFR, but only degrades EGFR mutant variants.

CRAF dimerization with ARAF regulates KRAS-driven tumor growth.

KRAS, which is mutated in ∼30% of all cancers, activates the RAF-MEK-ERK signaling cascade. CRAF is required for growth of KRAS mutant lung tumors, but the requirement for CRAF kinase activity is unknown. Here, we show that subsets of KRAS mutant tumors are dependent on CRAF for growth.

Structure-based optimization of hydroxylactam as potent, cell-active inhibitors of lactate dehydrogenase.

Structure-based design was utilized to optimize 6,6-diaryl substituted dihydropyrone and hydroxylactam to obtain inhibitors of lactate dehydrogenase (LDH) with low nanomolar biochemical and single-digit micromolar cellular potencies. Surprisingly the replacement of a phenyl with a pyridyl moiety in the chemical structure revealed a new binding mode for the inhibitors with subtle conformational change of the LDHA active site. This led to the identification of a potent, cell-active hydroxylactam inhibitor exhibiting an in vivo pharmacokinetic profile suitable for mouse tumor xenograft study.

Identifying transcriptional programs underlying cancer drug response with TraCe-seq.

Genetic and non-genetic heterogeneity within cancer cell populations represent major challenges to anticancer therapies. We currently lack robust methods to determine how preexisting and adaptive features affect cellular responses to therapies. Here, by conducting clonal fitness mapping and transcriptional characterization using expressed barcodes and single-cell RNA sequencing (scRNA-seq), we have developed tracking differential clonal response by scRNA-seq (TraCe-seq).

The promise and peril of KRAS G12C inhibitors.

RAS mutant tumors have been largely refractory to therapies until now. Recent findings published in the New England Journal of Medicine show that sotorasib provides clinical benefit for KRAS p.G12C-mutated non-small-cell lung cancer (NSCLC) and provide mechanistic insights into acquired resistance to KRAS-specific inhibition.

Targeting KRAS Mutant Cancers via Combination Treatment: Discovery of a Pyridopyridazinone pan-RAF Kinase Inhibitor.

Structure-based optimization of a set of aryl urea RAF inhibitors has led to the identification of Type II pan-RAF inhibitor GNE-9815 (), which features a unique pyrido[2,3-]pyridazin-8(7)-one hinge-binding motif. With minimal polar hinge contacts, the pyridopyridazinone hinge binder moiety affords exquisite kinase selectivity in a lipophilic efficient manner. The improved physicochemical properties of GNE-9815 provided a path for oral dosing without enabling formulations.

ARAF mutations confer resistance to the RAF inhibitor belvarafenib in melanoma.

Although RAF monomer inhibitors (type I.5, BRAF(V600)) are clinically approved for the treatment of BRAF-mutant melanoma, they are ineffective in non-BRAF mutant cells. Belvarafenib is a potent and selective RAF dimer (type II) inhibitor that exhibits clinical activity in patients with BRAF- and NRAS-mutant melanomas.

Emerging Trends in Cancer Drug Discovery-From Drugging the "Undruggable" to Overcoming Resistance.

Technology advancement and the courage to challenge dogma have been key elements that have continuously shifted druggability limits. We illustrate this notion with several recent cancer drug-discovery examples, while also giving an outlook on the opportunities offered by newer modalities such as chemically induced proximity and direct targeting of RNA. Treatment resistance is a major impediment to the goal of durable efficacy and cure, but the confluence of new biological insights, novel drug modalities, and drug combinations is predicted to enable transformative progress in this decade and beyond.

Targeting KRAS Mutant Cancers via Combination Treatment: Discovery of a 5-Fluoro-4-(3)-quinazolinone Aryl Urea pan-RAF Kinase Inhibitor.

Optimization of a series of aryl urea RAF inhibitors led to the identification of type II pan-RAF inhibitor GNE-0749 (), which features a fluoroquinazolinone hinge-binding motif. By minimizing reliance on common polar hinge contacts, this hinge binder allows for a greater contribution of RAF-specific residue interactions, resulting in exquisite kinase selectivity. Strategic substitution of fluorine at the C5 position efficiently masked the adjacent polar NH functionality and increased solubility by impeding a solid-state conformation associated with stronger crystal packing of the molecule.

Machine-Learning and Chemicogenomics Approach Defines and Predicts Cross-Talk of Hippo and MAPK Pathways.

Hippo pathway dysregulation occurs in multiple cancers through genetic and nongenetic alterations, resulting in translocation of YAP to the nucleus and activation of the TEAD family of transcription factors. Unlike other oncogenic pathways such as RAS, defining tumors that are Hippo pathway-dependent is far more complex due to the lack of hotspot genetic alterations. Here, we developed a machine-learning framework to identify a robust, cancer type-agnostic gene expression signature to quantitate Hippo pathway activity and cross-talk as well as predict YAP/TEAD dependency across cancers.

Author Correction: RAS-targeted therapies: is the undruggable drugged?

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Dimerization Induced by C-Terminal 14-3-3 Binding Is Sufficient for BRAF Kinase Activation.

The Ras-RAF-MEK-ERK signaling axis, commonly mutated in human cancers, is highly regulated to prevent aberrant signaling in healthy cells. One of the pathway modulators, 14-3-3, a constitutive dimer, induces RAF dimerization and activation by binding to a phosphorylated motif C-terminal to the RAF kinase domain. Recent work has suggested that a C-terminal "DTS" region in BRAF is necessary for this 14-3-3-mediated activation.

Negative regulation of RAF kinase activity by ATP is overcome by 14-3-3-induced dimerization.

The RAS-RAF-MEK-ERK signaling axis is frequently activated in human cancers. Physiological concentrations of ATP prevent formation of RAF kinase-domain (RAF) dimers that are critical for activity. Here we present a 2.

Partners in Crime: Clandestine Operations among RAS-RAF Accomplices in Promoting Tumorigenesis.

In this issue of Molecular Cell, Terrell et al. (2019) characterize the interactions of RAS-RAF complexes in live cells. Using bioluminescence resonance energy transfer (BRET) technology, they show that individual RAF family members exhibit distinct binding affinities to each RAS family protein, with CRAF exhibiting high binding affinities for all RAS proteins and BRAF exhibiting increased binding affinity for KRAS.

Pharmacological Induction of RAS-GTP Confers RAF Inhibitor Sensitivity in KRAS Mutant Tumors.

Targeting KRAS mutant tumors through inhibition of individual downstream pathways has had limited clinical success. Here we report that RAF inhibitors exhibit little efficacy in KRAS mutant tumors. In combination drug screens, MEK and PI3K inhibitors synergized with pan-RAF inhibitors through an RAS-GTP-dependent mechanism.

Targeting the MAPK Pathway in RAS Mutant Cancers.

Despite decades of extensive drug discovery efforts, there are currently no targeted therapies approved to treat KRAS mutant cancers. In this review, we highlight the challenges and opportunities in targeting KRAS mutant tumors through inhibition of mitogen-activated protein kinase (MAPK) signaling with conformation-specific kinase inhibitors. Through structural analysis and mechanistic studies with BRAF and mitogen-activated protein kinase (MEK) inhibitors, we describe how kinase-dependent and -independent functions of MAPK signaling components regulate KRAS-driven tumorigenesis and how these insights can be used to treat RAS mutant cancers with small molecule kinase inhibitors.

Tissue-Specific Mutations in BRAF and EGFR Necessitate Unique Therapeutic Approaches.

A predominant number of cancers are driven by mutations of key growth signaling genes. While it might be expected that the same alterations within a given oncogene would be identified in all tissues, there are clear cases of tissue specificity. Here, we highlight the tissue specificity of BRAF and EGFR alterations and implications for therapeutic targeting.

The RAS/MAPK Axis Gets Stressed Out.

In this issue of Molecular Cell, Ritt et al. (2016) describe a stress-induced checkpoint that effectively suppresses RAS-MAPK signaling. This pathway, activated by agents such as Rigosertib that induce mitotic and oxidative stress, results in JNK-mediated inhibition of RAS-MAPK pathway components SOS and RAF.

Discovery of a Noncovalent, Mutant-Selective Epidermal Growth Factor Receptor Inhibitor.

Inhibitors targeting the activating mutants of the epidermal growth factor receptor (EGFR) have found success in the treatment of EGFR mutant positive non-small-cell lung cancer. A secondary point mutation (T790M) in the inhibitor binding site has been linked to the acquired resistance against those first generation therapeutics. Herein, we describe the lead optimization of a series of reversible, pan-mutant (L858R, del T790M/L858R, and T790M/del) EGFR inhibitors.